Collector for electron beam tube



Jan. 4, 1966 M. E. LEVIN COLLECTOR FOR ELECTRON BEAM TUBE Filed April 9,1962 IN V EN TOR.

MART/N E, LEVIN ATTORNEY United States Patent 0 3,227,994 CGLLECTGR FORELECTRON BEAM TUBE Martin E. Levin, Millbrae, (Ialifi, assignor toEitel- McEullough, Inc, San Carlos, Calif a corporation of CaliforniaFiled Apr. 9, 1962, Ser. No. 185,966 4 Claims. (Cl. 313-21) Thisinvention relates to collector electrodes for electron beam tubes, andparticularly to a fluid cooled collector electrode.

Collector electrodes for high power electron beam tubes are usuallyfabricated from one or more copper billets hollowed to provide a chamberwithin which the electron beam is trapped. The exterior of the billetsare sometimes provided with spiral channels for the passage of fluidcoolant around the collector to effect a transfer or" heat from themetallic collector block to the fluid coolant. Collectors fabricated inthis manner are frequently either difficult to fabricate and thereforeexpensive, or are inefficient. Accordingly, it is one of the importantobjects of the present invention to provide a collector which iseconomical to manufacture and relatively inexpensive, and which isextremely efiicient in the dissipation of heat.

High power electron beam tube collectors which are required to dissipatelarge amounts of power are usually large in physical dimensions, andrequire the passage therethrough of large volumes of fluid coolant toeffectively dissipate the required power. Such collectors also requirethat substantial pressure he applied on the fluid coolant in order toprovide the required velocity to effect efficient heat transfer. It istherefore another of the objects of this invention to provide a compactcollector utilizing a relatively small volume of fluid coolant atrelatively low pressure but with sufiicient velocity to provideturbulent flow.

Another problem often encountered is the tendency to develop zones ofunequal heating and heat conduction through the metallic collectorblock. It is therefore a still further object of the invention toprovide a collector in which there is substantial uniformity of heatconduction through the metallic collector block and uniformity of heattransfer from the collector block to the fluid coolant.

Most conventional collectors for electron beam tubes are constructed soas to provide a high volume of fluid coolant through the collector witha small rise in the coolant temperature and without regard to otherfactors controlling hydraulic turbulence. This practice is said to bejustified by the fact that when there is only a small rise in the fluidcoolant temperature, the fluid coolant may be admitted to the collectorat a higher temperature; as a consequence of the higher inlettemperature, a smaller heat transfer unit may be utilized to cool thefluid coolant after it has left the collector. However, if the collectorcan be designed to use a greater differential between inlet and outlettemperatures and simultaneously allows a high inlet temperature and lowflow rate, a very efiicient collector will result. It is accordinglyanother object of the present invention to provide a collector which isrelatively small in physical dimensions, which operates at a relativelygreat disparity between the inlet and outlet temperatures, whichpossesses a low volume flow, and which permits high inlet temperatures.

Another important consideration in the design of a collector electrodefor an electron beam tube utilizing a re-entrant magnetic circuit is theoutside diameter of the collector. Most conventional electron beam tubesre quire a magnetic circuit to radially confine the electron beam. Withtubes using a re-cntrant magnetic circuit,

the diameter of the collector has a twofold effect on the size andefficiency of the magnetic circuit. First, the magnetic field strengthobtained from a coil depends di rectly on its mean diameter which isdetermined in part by the diameter of the collector which the coil mustsurround. Second, the total gap field of the magnetic circuit depends onthe area of the magnetic pole piece, which is again a function of thecollector diameter where a pole piece forms an integral part of the tubeassembly. It is therefore another important object of the presentinvention to provide a collector electrode having a small diameter inroportion to the amount of power which it dissipates.

During operation of an electron tube equipped with a fluid cooledcollector, the coolant flow rate in terms of volume should be as smallas possible With a reasonable pressure drop in the coolant system. It isalso desirable that the fluid coolant passages be of simple anduncomplicated configuration so as to eliminate difliculties attendant tofabrication of the collector. It is therefore a still further object ofthe present invention to provide a collector which utilizes simplyformed longitudinally extending parallel passageways for passage of thefluid coolant.

The invention possesses other objects and features of value, some ofwhich, with the foregoing, will be apparent from the followingdescription and the drawings. it is to be understood, however, that theinvention is not limited to the embodiment illustrated and described, asthe invention may be embodied in various forms within the scope of theappended claims.

Broadly considered, the collector construction of the inventioncomprises an elongated metallic block, preferably of copper and havingan interior chamber within which the electron beam is adapted toimpinge. Around its exterior periphery the collector block is providedwith a plurality of longitudinally extending passageways constituted bycircumferentially spaced radially extending fins formed by millinggrooves in the outer peripheral surface of the collector block. The finslie parallel to each other and parallel to the axis of the collector. Atone end the collector block is provided with an annular manifold plateor block having a chamber therein and a plurality of radially extendingpassageways forming a set thereof communicating the manifold chamberwith specific passageways or grooves formed in the circumferentialperiphery of the collector, groups of these latter being arranged insets, each set comprising a plurality of longitudinally extendingpassageways, one of which is designated an inlet passageway and anotheran outlet passageway with the radial passageways in the manifold plateconnecting the inlet passageways of each set. Other longitudinallyextending passageways formed in the manifold plate communicate with theoutlet passageways of the circumferentially spaced collector blockpassageways. A fluid coolant admitted to the chamber flows from themanifold chamber into the longitudinally extending parallel inletpassageways. After coursing in parallel the length of the collectorblock through the inlet passageways, the fluid coolant flows into thenext adjacent pas sageway of the set which channels it in the oppositedirection to again traverse the length of the collector block, afterwhich it flows in opposite directions in the next two passagewaysconstituting the set, from the last one of which, designated an outletpassageway, the coolant again flows through the manifold plate and exitsfrom the collector. It will thus be seen that a multiplicity of sets ofcoolant passageways are provided, with the passageways in each setconnected in series and with the sets of passageways connected inparallel. This interconnection of the collector passageways with themanifold plate to permit parallel interconnection has the beneficialeffect of causing the heat to distribute evenly throughout the collectorblock, and also effects a uniform heat transfer from the metallic wallof the collector to the fluid coolant. To channel the fluid coolantserially through the proper passageways, the exterior peripheralcylindrical surface of the collector block is sealed into a cylindricalstainless steel sleeve which fits in a fluid-tight shrink-fit closelyabout the outer peripheral edges of the fins or lands which form thecollector passageways.

Because it is desirable that electrons that enter the hollow collectorbe trapped therein, and that secondary electrons liberated by highvelocity primary electrons also be trapped within the collector, theopen or input end of the hollow collector block is provided with asecondary electron suppressor shield or baflle plate to prevent egressof electrons from the collector and impingement on the body of theelectron tube. Means are also provided electrically insulating theconductive collector block from the adjacent electron tube body.

Referring to the drawings:

FIGURE 1 is a vertical cross-sectional view disclosing the interiorconstruction of the collector. Portions of the structure are inelevation to disclose the interconnection of the collector block coolantpassageways.

FIGURE 2 is a horizontal cross-sectional view taken in the planeindicated by the line 2--2 in FIGURE 1. The view illustrates therelationship of groove depth, fin thickness and wall thickness of thecollector.

FIGURE 3 is a horizontal cross-sectional view taken in the planeindicated by the line 33 in FIGURE 1. The view illustrates therelationship between adjacent parallel sets of passageways extendinglongitudinally of the collector block.

FIGURE 4 is a horizontal sectional view taken in the plane indicated bythe line 4-4 in FIGURE 1. The view illustrates the radially andlongitudinally extending slots or passageways formed in the manifoldplate for interconnecting respectively, the inlet and outlet passagewaysof the collector.

FIGURE 5 is a horizontal cross-sectional view taken through the manifoldplate, the section being taken in the plane indicated by the line 55 ofFIGURE 4.

All of the figures are drawn approximately actual size.

In the design ofan-eflicient collector for an electron beam tube, one ofthe first considerations is the power density distribution of the beamafter it has entered the collector. Conveniently, the power densitydistribution of the beam within the collector is proportional to thepower density distribution of the electron beam before it enters thecollector. This enables close approximation of the power density ofimpingement of the electron beam within the collector, the insidediameter and configuration of the collector surface against which theelectrons impinge being selected with due consideration to the impingingpower density and the total power required to be dissipated. Ideally,the inner surfaces of the collector block will possess a curvedconfiguration providing a constant impinging power density over anappreciable length of collector. Such a surface is extremely difficultto ma chine, and is costly in time and money. It is possible andpracticable, however, to approximate such a curved surface by formationof a part of the collector block in a single or plurality of axiallyaligned portions having their interior surfaces conically tapered towardthe axis of the collector.

With the inside diameter of the collector block a known factor, and withthe thermal conductivity of copper and the power to be dissipated alsoknown, it is possible to determine the length of the collector whichwill dissipate with a reliable margin of safety the heat generated inthe collector by impingement of the electron beam notwithstanding thefact that the interior surfaces of the collector block only approximatea configuration which would provide a constant impinging power density.

Since it is desired to transfer the heat so generated into a suitablefluid coolant, it is important that the temperature of the copper remainbelow the critical temperature at which boiling of the fluid coolantoccurs, it being noted that this critical temperature is dependent onseveral facors such as coolant used, pressure and velocity. The heattransfer through the collector block and into the fluid coolant isproportional to the temperature of the copper less the temperature ofthe fluid coolant. Heat transfer is also proportional to the velocity ofthe fluid coolant flowing through the passageways, and is inverselyproportional to the hydraulic diameter of the passageways themselves.

The velocity and hydraulic diameter of the passageways is importantbecause these factors, with pressure, control the total amount of fluidcoolant required in the system and determine also whether the flow ofthe fluid coolant is laminar or turbulent. Turbulent flow and notlaminar flow is preferred because heat transfer is more efiicient withturbulent flow. Since the amount of power which must be dissipated perunit area of collector surface is known, and since the flow rate involume of fluid coolant for a given system is more or lessdiscretionary, it is desirable that heat transfer efficiency of thecollector be optimized for a reasonably small volume of fluid coolant byincreasing the surface area over which the fluid coolant will flow.

The collector of this invention therefore comprises a longitudinallyextending hollow metallic body symmetrical about a longitudinal axis,and having a first hollow cylindrical body portion 2, having acylindrical interior surface 3 formed therein, and a multiplicity oflongitudinally extending collector block passageways 4 formed in itsouter periphery at circumferentially equally spaced intervals. Thepassageways 4 are defined by longitudinal radially extending fins 7,left projecting from the cylindrical surface of the collector block bythe milling operation which forms the passageway 4. The fins may ofcourse be formed by a hobbing operation or as extrusions. At one end ofthe tubular collector block portion 2, the end portions of alternatefins 7 are milled away as shown at 8 in FIGURE 1, to provide aconnection at this end of the collector of two adjacent passagewaysforming a pair. From FIGURE 1 it will be seen that adjacent pairs arecircumferentially spaced about the collector block and that theintermediate fin 7 between the adjacent pairs of connected passagewaysprevents flow of fluid coolant from one pair to the other at this end ofthe collector. Instead of being milled away a depression may be formedin flange 23 opposite the end of a fin to provide intercommunicationbetween two adjacent passageways forming a pair.

At the other end, the collector block 2 is closed by a terminal or endblock collector portion 13, having conically tapered interior walls 14defining a hollow chamber 16 communicating at one end with the collectorportion 2 and closed at its opposite end by wall 17. The exteriorcylindrical surface of the collector end block portion 13 is milled toprovide the same number and spacing of fins as in collector blockportion 2. The collector blocks 2 and 13 are brazed at the jointure line18 so that the fins align themselves to provide continuous passagewaysover the entire length of the collector. At the end of collector block13 adjacent end Wall 17 thereof, every fifth fin is milled away asindicated at 19 in FIG- URE 1 so that also at this end of the collectortwo adjacent passageways 4 are serially interconnected to form a pair,one passageway of this pair constituting one of the passageways of thepair thereof discussed with respect to the other end of the collector.In this way four adjacent passageways are serially interconnected toform one set of four passageways. As shown in FIGURE 1, the outerpassageways of each set form inlet and outlet passageways, with theinlet passageway of each set being next adjacent the outlet passagewayof the next adjacent set of passageways. For increased efficiency andreduction of the pressure drop through the system, the inlet and outletpassageways are charnfered at their ends adjacent the collector end wallas shown at 29. The inlet passageways may collectively be considered aset of inlet passageways and the outlet passageways may collectively beconsidered a set of outlet passageways.

Thus, in the embodiment illustrated, at each twentyfour degree intervalabout the collector, a fin extends the entire length of the collector,while of the three fins therebetween, the two outside fins are milledaway at one end adjacent the input end of the collector while theremaining fin between these two is milled away at the opposite or closedend of the collector. Two adjacent full length fins thus define betweenthem a set of passageways.

In order that fluid coolant may progress through the passageways, theentire collector block is enclosed within a stainless steel sleeve 21which forms a shrink-fit about the outer ends of the fins. At its inputend, the collector is provided with a cylindrical member 22, having aradially extending flange 23 brazed within the end of the sleeve. Theflange also abuts the end of the tubular portion 2, and is brazedthereto in a fluid-tight manner. At its opposite end, the tubular member22 is provided with a truncated hollow conical secondary electronsuppression shield or baflle plate 24 having its large base brazed toone end of the tubular member 22, and having an aperture 26 at its apexend through which the beam enters the collector body. As shown in FIGURE1, the aperture in the apex end of the suppressor shield is materiallysmaller than the inner diameter of either the tubular member 22 or thecollector portion 2. The aperture is preferably proportioned to closelysurround the beam after it passes the last interaction gap and before itspreads materially, which eflect occurs after the beam has passed intothe collector where the electrons spread outwardly and impinge upon theinner surface of the collector as indicated by the dash lines 27. Asoften happens, the primary electrons entering the collector will releasesecondary electrons from the walls of the collector. With the presentdesign of the secondary electron suppressor plate or shield, thesesecondary electrons impinge on the shiled plate and do not impinge uponthe body of the electron tube as would be the case in the absence of theshield plate. Since the collector electrode is electrically insulatedfrom the radio frequency body structure 28 of the electron tube by thesealing means 29 illustrated in FIGURE 1, electrons which impinge uponthe suppressor shield have no effect on either the temperature or thebody current of the electron tube, the value of the latter of which isan excellent indication of the percentage beam current being interceptedby the body of the electron tube.

To admit a fluid coolant into the collector passageways, an annularmanifold plate 31 is superposed over and brazed to the closed end wall17 of the collector block 13 within the cylindrical sleeve 21. Themanifold plate is brazed about its outer periphery within the sleeve,and is provided with a central aperture 32, rabbeted as shown, toreceive the inner end of an inlet conduit 33. Adjacent the opposite faceof the manifold plate the central aperture is increased in diameter andcommunicates with a manifold chamber 34, having a plurality of radiallyextending slots 36 milled in the manifold plate between the innerperiphery of the centrally disposed manifold chamber and the outerperpihery of the manifold plate. As shown best in FIG- URE 4, there areconveniently fifteen such passageways connecting the manifold chamberwith the exterior periphery of the manifold plate.

The passageways 36 are circumferentially equally spaced about themanifold plate and constitute inlet passages connected to selected onesof the passageways 4 constituting inlet passageways in each set of fourpassageways and which extend longitudinally along the periphery of thecollector block as discussed above. As shown in FIGURES l and 5, theradially extending grooves 36 do not extend longitudinally through theentire depth of the plate 31, but rather extend only to a depthcorreponding to the depth of the manifold chamber 34.

Also milled into the manifold plate are a multiplicity of slots orpassageways 37 which do extend longitudinally through the manifoldplate. These passageways, as shown best in FIGURES 1, 4 and 5, extendthrough the thickness of the manifold plate and extend radially for adistance, but not suificiently to communicate the inner and outerperipheries of the plate. In the structure illustrated, there arepreferably fifteen such passageways 37, each connecting a selected oneof the outlet passageways 4 formed in the collector block. It will thusbe seen that by orienting the manifold plate so that one of the inletslots 36 registers with a selected one of the inlet passages 4 in thecollector block, fluid coolant will be caused to flow in parallelthrough the sets of passageways, and serially through adjacentpassageways 4 in each set. This occurs by virtue of the fact that theinlet slots 36 are spaced circumferentially 24 apart about the manifoldplate 31, and the passageways 4 in the collector block arecorrespondingly spaced.

As viewed in FIGURE 1, therefore, the fluid coolant will flow from thechamber 34 radially outwardly through the radially extending slots 36into the longitudinally extending inlet passageways 4 which areregistered with the associated slots 36. Fluid coolant will then flow inthe same direction through all the inlet passageways 4 longitudinally ofthe collector block as shovm best by the arrows in FIGURE 1.

As the fluid coolant comes to the end of the fin at the input end of thecollector which has been milled away as at 8, the fluid coolant ischanneled around the fin 7 by the flange 23 and progresses in theopposite direction through the next adjacent passageway 4, until itreaches the opposite end of the collector block and the area 19 producedby milling away the end of another of the fins 7, at this endconstituting every fourth one. The fluid coolant flows around the end ofthe fin, channeled by the flat surfaces 38 of the manifold plate, andflows the length of the collector block again, and is again directed orchanneled into the next adjacent passageway by another area 8 formed asbefore by milling away the end of the fin.

In its fourth and last passage over the length of the collector block,the fluid coolant exits from the fourth or outlet passageway into one ofthe passageways 37 which communicates with an annular chamber 39 definedbetween plate 31, sleeve 21 and a closure plate 41, the chamber 39functioning to combine the fluid coolant from all of the outletpassageways 37 and discharge the fluid coolant into the outlet conduit42.

It will thus be seen that the longitudinally extending passageways 4surrounding the collector block are arranged in a plurality ofcircumferentially spaced sets, there being 15 such sets spaced 24 apartabout the outer periphery of the collector block in the embodimentillustrated. Each set of passageways is connected in parallel with theremaining sets through the medium of the collector manifold chamber 34and associated inlet passageways 36. Each set is also connected inparallel with the remaining sets by outlet passageways 37 connected witheach associated set and combining the outflow from each set into acommon chamber 39.

Within each set, there are four passageways, two of the passagewayscarrying the fluid coolant in one direction longitudinally of thecollector, and the remaining two passageways of the set carrying thefluid in the opposite direction. As shown by the arrows in FIGURE 1,within each set the direction of flow reverses in adjacent passageways.In this manner fluid coolant admitted to each set of passageways at theclosed end of the collector block egresses from that particular set atthe same end of the collector block. This facilitates connection of thecollector to a coolant system.

Another advantage of this arrangement is that it places the outletpassageway for each set next adjacent the inlet passageway for the nextset. In this manner, the coldest fluid coolant entering the system isplaced next adjacent the outlet passage carrying the hottest fluidcoolant. This arrangement ensures that as the hottest portion of thecoolant egresses from the collector cooling system, the fins whichdefine this outlet passageway will remain at a temperature below thecritical temperature previously defined. The arrangement thus minimizesnon-uniformity in the distribution of heat through the collector block.

In the manufacture of the electron tube collectors which utilize thickbillets of copper to form collector block portions, it has been foundthat the copper blocks are often defective in that in the process ofmanufacture of the blocks, pipes or longitudinally extending passagewaysare formed in the copper which permit the passage of air. In aconstruction such as that illustrated, where a relatively short block 13is provided with a conical depression 16 closed by a relatively thinwall 17, such pipes may extend from the interior of the collector to anexterior surface thereof. In the collector illustrated, in order topreclude the pipes from forming a passageway for air between theexterior and the interior of the collector, the end of the collectorblock 13 next adjacent the manifold plate is provided with a copper sealplate 44 fabricated so that its grain structure lies in a directionperpendicular to the grain structure of the block 13. The plate ispreferably brazed in a recess formed in the end of the collector block13 and possesses a thickness suflicient to provide a projecting portionas shown useful as a guide to center the manifold plate over the end ofcollector block.

It will thus be seen that for eflicient operation of the collector, itis important that the cylindrical sleeve 21 which surrounds thepassageways 4 and fins 7 be united to the ends of the fins in afluid-tight manner to confine the flow of fluid coolant in the desiredpassageways. To accomplish this, the fins 7 and passageways 4 arepreferably silver plated, and so is the interior surface 43 of thesleeve 21. The sleeve is then assembled onto the collector block byshrink-fitting the sleeve 21 thereon. The entire assembly is then passedthrough a brazing furnace to effect brazing of the sleeve to flange 23and plate 41. In this operation the silver plate and the copper of thefins 7 form a eutectic which brazes the outer edge of each fin 7 to theinner surface 43 of the sleeve 21 in a watertight manner.

In operation, it has been found that a collector fab ricated accordingto this invention is capable of efliciently dissipating at least 70 kw.of power. In the structure shown, the heat transfer capacity is designedto be about one kilowatt per square inch of collector surface. It hasbeen found that this power dissipation is conveniently etfected withfins that are A; of an inch high, spaced at equal intervals about theouter periphery of the collector block and arranged in parallel sets asdiscussed above. The spacing of the grooves and fins at whole numberdegrees about the outerperiphery of the collector block is important inthat it greatly facilitates milling of the collector block's. When finsare spaced whole number degrees apart, the indexing guide or head of themilling machine on which the collector is milled may be set directlywithout consideration of fractions of degrees. This greatly increasesuniformity of fin dimension, facilitates fabrica tion, and lessens thetime spent in milling the collector, with an attendant saving in cost.

I claim:

1. In an electron tube, a fluid-cooled electrode element comprising ahollow body having a cylindrical side wall disposed about a longitudinalaxis, a multiplicity of elongated circumferentially spaced parallelprojections on the cylindrical side wall defining axially extendingchannels through which a fluid coolant may flow, elected ones of saidcircumferentially spaced projections defining noncommunicating sets ofsaid channels, two adjacent of said selected projections having disposedtherebetween three intermediate projections arranged to provide two pairof adjacent parallel channels serially intercommunicated with eachother, jacket means surrounding said body to enclose said channels, andmeans connecting the separate sets of channels in parallel connectionwith a source of fluid coolant.

2. The combination according to claim 1, in which one end of one of saidthree intermediate projections adjacent one end of the body is axiallyspaced from the associated ends of the adjacent selected ones of saidprojections.

3. The combination according to claim 1, in which one channel in eachset constitutes an inlet channel and another channel in each setconstitutes an outlet channel, the inlet channel of each set beingdisposed on one side of each respective selected projection and beingcircumferentially spaced next adjacent the outlet channel of the nextadjacent set of channels which is located on the other side of theselected projection.

4. A fluid-cooled electrode for an electron tube comprising a hollowbody having a cylindrical side wall disposed about a longitudinal axisand an end wall closing one end of the hollow body, a multiplicity ofelongated parallel passageways extending axially through the side walladjacent the outer cylindrical periphery thereof and through which afluid coolant may flow, said passageways being arranged in at least twoseparate sets of passageways, each set having four of said passagewaysincluding an inlet and an outlet passageway, and means adjacent one endof the hollow body connecting in parallel the inlet passageways of theseparate sets and connecting in parallel the outlet passageways of theseparate sets.

References Cited by the Examiner UNITED STATES PATENTS 2,871,397 1/1959Preist et al. 3155.46 3,098,165 7/1963 Zitelli 3132l DAVID J. CALVIN,Primary Examiner.

1. IN AN ELECTRON TUBE, A FLUID-COOLED ELECTRODE ELEMENT COMPRISING AHOLLOW BODY HAVING A CYLINDRICAL SIDE WALL DISPOSED ABOUT A LONGITUDINALAXIS, A MULTIPLICITY OF ELONGATED CIRCUMFERENTIALLY SPACED PARALLELPROJECTIONS ON THE CYLINDRICAL SIDE WALL DEFINING AXIALLY EXTENDINGCHANNELS THROUGH WHICH A FLUID COOLANT MAY FLOW, SELECTED ONES OF SAIDCIRCUMFERENTIALLY SPACED PROJECTIONS DEFINING NONCOMMUNICATING SETS OFSAID CHANNELS, TWO ADJACENT OF SAID SELECTED PROJECTIONS HAVING DISPOSEDTHEREBETWEEN THREE INTERMEDIATE PROJECTIONS ARRANGED TO PROVIDE TWO PAIROF ADJACENT PARALLEL CHANNELS SERIALLY INTERCOMMUNICATED WITH EACHOTHER, JACKET MEANS SURROUNDING SAID BODY TO ENCLOSE SAID CHANNELS, ANDMEANS CONNECTING THE SEPARATE SETS OF CHANNELS IN PARALLEL CONNECTIONWITH A SOURCE OF FLUID COOLANT.